The commercial briquetting of the fine coal that is typically discarded from a coal-preparation plant is hindered by its high and difficult to remove moisture content. When attempting to form briquettes directly from this material, the poor flow properties of the high-moisture coal fines dictates a relatively slow production rate as well as inconsistencies in the briquetter feed rate and frequent run stoppages. This equates to increased operating costs and variable briquette quality. Further, the briquettes produced without the addition of a cost-prohibitive amount of binder have low green strengths requiring that they be cured before they are suitable for handling and transport.
Thermal drying of a fine coal prior to briquetting solves these problems but such a drying step is both expensive and problematic. The current method of choice for drying wet coal fines is a fluidized bed dryer. However, such units are potentially dangerous and can be difficult to permit when applied to a combustible material such as coal fines as thermal drying can generate an explosive dust that is difficult to contain. Alternate methods of thermal drying, i.e. a conveyed or static bed, are inefficient and suffer to a lesser degree from the same safety and dust containment concerns. Drying at ambient temperatures is not commercially practical due to a prohibitively low rate of evaporation of the moisture from a bulk sample of wet fine coal.
The present invention addresses and solves these problems allowing the production of high-quality, low-moisture briquettes from high-moisture fine coal, such as that discarded in the waste-stream slurry at a coal preparation plant, or from blends of wet fine coal and biomass in a manner that is less expensive and safer than current technologies.